title: C/EBP homology protein (CHOP) interacts with activating transcription factor 4 (ATF4) and negatively regulates the stress-dependent induction of the asparagine synthetase gene.
abstract: C/EBP homology protein (CHOP), a stress-induced transcription factor, is involved in transcriptional regulation, cell cycle, and apoptosis. The present studies identified CHOP as an interacting partner of activating transcription factor (ATF) 4 in a yeast two-hybrid screen and confirmed their interaction in HEK293T cells. CHOP protein levels rose modestly and transiently during amino acid deprivation, whereas endoplasmic reticulum stress caused a much higher and sustained expression of CHOP protein. Exogenous CHOP expression enhanced the TRB3 gene induction by amino acid deprivation. Conversely, CHOP suppressed the induction of the endogenous asparagine synthetase (ASNS) gene and inhibited transcription from a reporter gene driven by the ASNS promoter following activation by ATF4 or amino acid deprivation. Short interfering RNA-mediated knockdown of CHOP further enhanced the induction of ASNS by either amino acid deprivation or endoplasmic reticulum stress. The CHOP-dependent repression of the ASNS gene required the entire CHOP protein, arguing against the possibility of simple sequestration of ATF4 by the CHOP leucine zipper domain, and chromatin immunoprecipitation analysis showed association of CHOP with the ASNS and TRB3 promoters. Interestingly, chromatin immunoprecipitation also showed that CHOP was associated with the C/EBP-ATF composite site regions of the SNAT2, VEGF, and CAT-1 genes, despite no significant effect on their expression after exogenous CHOP overexpression. Collectively, the results document that CHOP is a member of the transcription factor network that controls the stress-induced regulation of specific C/EBP-ATF-containing genes, such as ASNS.
authors.affiliation: Department of Biochemistry and Molecular Biology, Shands Cancer Center and Center for Nutritional Sciences, University of Florida College of Medicine, Gainesville, Florida 32610, USA.
authors.forename: Nan
authors.initials: N
authors.lastname: Su
authors.forename: Michael S
authors.initials: MS
authors.lastname: Kilberg
mesh_terms: D051701:Activating Transcription Factor 4 / Q000378:metabolism*; D017209:Apoptosis; D001217:Aspartate-Ammonia Ligase / Q000378:metabolism*; D001665:Binding Sites; D018797:Cell Cycle Proteins / Q000378:metabolism; D047369:Chromatin Immunoprecipitation; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism / Q000037:antagonists & inhibitors; D017434:Protein Structure, Tertiary; D034741:RNA, Small Interfering / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism; D051742:Transcription Factor CHOP / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: C497109:ATF4 protein, human; D018797:Cell Cycle Proteins; C497249:DDIT3 protein, human; D034741:RNA, Small Interfering; D012097:Repressor Proteins; C474831:TRIB3 protein, human; D051701:Activating Transcription Factor 4; D051742:Transcription Factor CHOP; D017346:Protein Serine-Threonine Kinases; D001217:Aspartate-Ammonia Ligase